Reconstructing Fibromyalgia in Complex Chronic Pain (FM): Longitudinal Causal Inquiry and Diagnostic Responsibility

Fibromyalgia remains inconsistently recognized, particularly with shared-symptom comorbidities across specialties. This paper reconstructs diagnosis as a longitudinal causal task through historical and case-derived analysis, tracing Mayo’s primary–secondary fibrositis distinction, Philip Kahler Hench’s preservation of causal inquiry at Scripps, and subsequent fibromyalgia criteria. Earlier reasoning separated syndrome recognition from determining whether another disease merely coexisted or drove or sustained the amplification state. Later classification improved recognition without resolving that causal question. The framework uses secondary fibromyalgia to describe an amplification state driven or sustained by underlying disease, distinguishing it from self-sustaining primary fibromyalgia and mere comorbid coexistence. Mild fibromyalgia may be missed when limited hypersensitivity, disability, flares, or medication requirements produce fewer diagnostic signals. Proposed severity levels and distinctions among flares, baseline drift, and runaway fibromyalgia organize longitudinal assessment. Fibromyalgia demonstrates why syndrome recognition alone cannot determine the relationship between shared symptoms and coexisting disease. Differential diagnosis must continue across specialties and time, preserving competing causal formulations, symptoms, objective findings, disease activity, treatment exposure and response, and responsibility for revision. The transferable proposition concerns longitudinal diagnostic responsibility rather than shared biology across complex conditions. The framework is offered for prospective evaluation; the index case does not establish prevalence, mechanism, or treatment efficacy.